// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/path_service.h"

#if defined(OS_WIN)
#include <windows.h>
#include <shellapi.h>
#include <shlobj.h>
#endif

#include "base/containers/hash_tables.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/synchronization/lock.h"
#include "build/build_config.h"

namespace base {

bool PathProvider(int key, FilePath* result);

#if defined(OS_WIN)
bool PathProviderWin(int key, FilePath* result);
#elif defined(OS_MACOSX)
bool PathProviderMac(int key, FilePath* result);
#elif defined(OS_ANDROID)
bool PathProviderAndroid(int key, FilePath* result);
#elif defined(OS_POSIX)
// PathProviderPosix is the default path provider on POSIX OSes other than
// Mac and Android.
bool PathProviderPosix(int key, FilePath* result);
#endif

namespace {

    typedef hash_map<int, FilePath> PathMap;

    // We keep a linked list of providers.  In a debug build we ensure that no two
    // providers claim overlapping keys.
    struct Provider {
        PathService::ProviderFunc func;
        struct Provider* next;
#ifndef NDEBUG
        int key_start;
        int key_end;
#endif
        bool is_static;
    };

    Provider base_provider = {
        PathProvider,
        NULL,
#ifndef NDEBUG
        PATH_START,
        PATH_END,
#endif
        true
    };

#if defined(OS_WIN)
    Provider base_provider_win = {
        PathProviderWin,
        &base_provider,
#ifndef NDEBUG
        PATH_WIN_START,
        PATH_WIN_END,
#endif
        true
    };
#endif

#if defined(OS_MACOSX)
    Provider base_provider_mac = {
        PathProviderMac,
        &base_provider,
#ifndef NDEBUG
        PATH_MAC_START,
        PATH_MAC_END,
#endif
        true
    };
#endif

#if defined(OS_ANDROID)
    Provider base_provider_android = {
        PathProviderAndroid,
        &base_provider,
#ifndef NDEBUG
        PATH_ANDROID_START,
        PATH_ANDROID_END,
#endif
        true
    };
#endif

#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
    Provider base_provider_posix = {
        PathProviderPosix,
        &base_provider,
#ifndef NDEBUG
        PATH_POSIX_START,
        PATH_POSIX_END,
#endif
        true
    };
#endif

    struct PathData {
        Lock lock;
        PathMap cache; // Cache mappings from path key to path value.
        PathMap overrides; // Track path overrides.
        Provider* providers; // Linked list of path service providers.
        bool cache_disabled; // Don't use cache if true;

        PathData()
            : cache_disabled(false)
        {
#if defined(OS_WIN)
            providers = &base_provider_win;
#elif defined(OS_MACOSX)
            providers = &base_provider_mac;
#elif defined(OS_ANDROID)
            providers = &base_provider_android;
#elif defined(OS_POSIX)
            providers = &base_provider_posix;
#endif
        }
    };

    static LazyInstance<PathData>::Leaky g_path_data = LAZY_INSTANCE_INITIALIZER;

    static PathData* GetPathData()
    {
        return g_path_data.Pointer();
    }

    // Tries to find |key| in the cache. |path_data| should be locked by the caller!
    bool LockedGetFromCache(int key, const PathData* path_data, FilePath* result)
    {
        if (path_data->cache_disabled)
            return false;
        // check for a cached version
        PathMap::const_iterator it = path_data->cache.find(key);
        if (it != path_data->cache.end()) {
            *result = it->second;
            return true;
        }
        return false;
    }

    // Tries to find |key| in the overrides map. |path_data| should be locked by the
    // caller!
    bool LockedGetFromOverrides(int key, PathData* path_data, FilePath* result)
    {
        // check for an overridden version.
        PathMap::const_iterator it = path_data->overrides.find(key);
        if (it != path_data->overrides.end()) {
            if (!path_data->cache_disabled)
                path_data->cache[key] = it->second;
            *result = it->second;
            return true;
        }
        return false;
    }

} // namespace

// TODO(brettw): this function does not handle long paths (filename > MAX_PATH)
// characters). This isn't supported very well by Windows right now, so it is
// moot, but we should keep this in mind for the future.
// static
bool PathService::Get(int key, FilePath* result)
{
    PathData* path_data = GetPathData();
    DCHECK(path_data);
    DCHECK(result);
    DCHECK_GE(key, DIR_CURRENT);

    // special case the current directory because it can never be cached
    if (key == DIR_CURRENT)
        return GetCurrentDirectory(result);

    Provider* provider = NULL;
    {
        AutoLock scoped_lock(path_data->lock);
        if (LockedGetFromCache(key, path_data, result))
            return true;

        if (LockedGetFromOverrides(key, path_data, result))
            return true;

        // Get the beginning of the list while it is still locked.
        provider = path_data->providers;
    }

    FilePath path;

    // Iterating does not need the lock because only the list head might be
    // modified on another thread.
    while (provider) {
        if (provider->func(key, &path))
            break;
        DCHECK(path.empty()) << "provider should not have modified path";
        provider = provider->next;
    }

    if (path.empty())
        return false;

    if (path.ReferencesParent()) {
        // Make sure path service never returns a path with ".." in it.
        path = MakeAbsoluteFilePath(path);
        if (path.empty())
            return false;
    }
    *result = path;

    AutoLock scoped_lock(path_data->lock);
    if (!path_data->cache_disabled)
        path_data->cache[key] = path;

    return true;
}

// static
bool PathService::Override(int key, const FilePath& path)
{
    // Just call the full function with true for the value of |create|, and
    // assume that |path| may not be absolute yet.
    return OverrideAndCreateIfNeeded(key, path, false, true);
}

// static
bool PathService::OverrideAndCreateIfNeeded(int key,
    const FilePath& path,
    bool is_absolute,
    bool create)
{
    PathData* path_data = GetPathData();
    DCHECK(path_data);
    DCHECK_GT(key, DIR_CURRENT); // << "invalid path key";

    FilePath file_path = path;

    // For some locations this will fail if called from inside the sandbox there-
    // fore we protect this call with a flag.
    if (create) {
        // Make sure the directory exists. We need to do this before we translate
        // this to the absolute path because on POSIX, MakeAbsoluteFilePath fails
        // if called on a non-existent path.
        if (!PathExists(file_path) && !CreateDirectory(file_path))
            return false;
    }

    // We need to have an absolute path.
    if (!is_absolute) {
        file_path = MakeAbsoluteFilePath(file_path);
        if (file_path.empty())
            return false;
    }
    DCHECK(file_path.IsAbsolute());

    AutoLock scoped_lock(path_data->lock);

    // Clear the cache now. Some of its entries could have depended
    // on the value we are overriding, and are now out of sync with reality.
    path_data->cache.clear();

    path_data->overrides[key] = file_path;

    return true;
}

// static
bool PathService::RemoveOverride(int key)
{
    PathData* path_data = GetPathData();
    DCHECK(path_data);

    AutoLock scoped_lock(path_data->lock);

    if (path_data->overrides.find(key) == path_data->overrides.end())
        return false;

    // Clear the cache now. Some of its entries could have depended on the value
    // we are going to remove, and are now out of sync.
    path_data->cache.clear();

    path_data->overrides.erase(key);

    return true;
}

// static
void PathService::RegisterProvider(ProviderFunc func, int key_start,
    int key_end)
{
    PathData* path_data = GetPathData();
    DCHECK(path_data);
    DCHECK_GT(key_end, key_start);

    Provider* p;

    p = new Provider;
    p->is_static = false;
    p->func = func;
#ifndef NDEBUG
    p->key_start = key_start;
    p->key_end = key_end;
#endif

    AutoLock scoped_lock(path_data->lock);

#ifndef NDEBUG
    Provider* iter = path_data->providers;
    while (iter) {
        DCHECK(key_start >= iter->key_end || key_end <= iter->key_start) << "path provider collision";
        iter = iter->next;
    }
#endif

    p->next = path_data->providers;
    path_data->providers = p;
}

// static
void PathService::DisableCache()
{
    PathData* path_data = GetPathData();
    DCHECK(path_data);

    AutoLock scoped_lock(path_data->lock);
    path_data->cache.clear();
    path_data->cache_disabled = true;
}

} // namespace base
